Method for the production of fine grained steel



United States Patent O 3,375,105 METHOD FOR THE PRODUCTION" on FINE GRAlNED STEEL Dunstan W. P. Lynch, Cambridge, Ohio, assignon t0. VanadiumCorporation of America,.New York, N.Y.,.

a corporation of Delaware N Drawing. Filed Oct. 22, 1965, Ser. No.502,476 6 Claims. (Cl. 75-129) ABSTRACT OF THE DISCLOSURE" Method ofproducing fine grained steel by adding to said steel prior to teeminganalloy containing aluminum and silicon and another alloy containingvanadium and silicon.

This invention relates toa novel method for treating molten steel toproduce fine grain size. in the fimshed;

product.

When carbon or alloy steel is heated above its transformationtemperature, it enters into asolid solu'tionphase known as austenite.Austenite is a crystalline structure and the size of the austenitecrystals or grains is a tune tion of the degree to which the steel isheated beyond the transformation temperature. As the temperatureincreases beyond the transformation temperature, the austenite grainesses, sucha hardening, normalizing andannealing; require that the steelbe heated to temperatures in excess of the transformation temperature,it is necessary to inhibit austenitic grain growth where a fine grainsize is desired' For example, carburizing steel for case hardening ismost commonly performed atabout 1700 F. which is well above thetransformation temperatureof the austenitic phase. Such steels mustremain fine grained after treatment. i

' Steels with large grains are termed coarse grained, while steels withsmall grains are termed fine grained. The

McQuaid-Ehn test is commonly used for determining the austenitic grainsize, and the ASTM grain size numbers 1 are normally used for rating thesteels. An ASTM rating of l to 5 is considered coarse, while an ASTMrating of 5 to 8 is considered fine. Grain size ratings finer than 8 iceHowever, there are many'cases'where the: additionof'. aluminum to the.steel is detrimental. For instance: trans verse'mechanical properties.ofplate products from such; steels are lower than longitudinal?mechanical properties, particularly in impact resistance. Anotherdetrimentalef-. fectgof aluminum is that it createsa poor. surfaceonthe: ingotor'wrought product and this-results in costly conditioning,poor formability or even rejection. Furthermore, aluminum cannot beadded to some grades of steel be-- cause it causes poor hot-workability.Still another detrim n l if ctof. aluminum has. recentlycome to.lightwith. the advent of continuous. casting, in. thatv the additionof.sufiicient aluminum to. the steel in. the. ladle to. produce a fine.grained steel causes. the molten. metal to solidify. in. the relativelysmall tundish nozzles.

It is known that the additionof. other elements, Such as vanadium,columbium, titanium, and zirconium, either singly or in combination,will produce fine grained steels. Apart from aluminum the element mostcommonly used for this purpose is vanadium. The amount of vanadiumnormally added, as ferrovanadium, is .Q 8% to .l5 While the use ofvanadium is eifective, it is relatively expensive, costing approximatelyten times more. per pound than aluminum.

My novel method is directed to the treatment of molten carbon and alloysteels to produce a high quality, fine grained steel; in thecast orWrought condition. The steel treated in accordance with my method maybecontinuously cast and retains its fine grain. structure at hightemperatures such as are encountered in high temperature carburizing.Additionally-, my method is. inexpensive since it, requires a very smallamount of vanadium.

I have discovered that the addition of a small amount of aluminum,insutficient by itself to produce fine grained steel, plus the additionof a much smaller amount of vanadium than that required to produce, finegrained steel when used alone inaccordance with previous practices, willproduce a fine grained steel.j In my novel method it is: essential thatthe, aluminum be added as an alloy containing both aluminum; and siliconrather than as aluminum metal. Additionally, it is essential in mymethod that the vanadium be added as an alloy containing vanadium mayalso occur. It is to be understood that the term fine grained steel,when used hereinafter, refers to steel having an ASTM number of 5 to 8and finer as determined by the McQuaid-Ehn grain size test, unlessotherwise specified.

Fine grained heat treated steels are normally preferred.

over coarse grained steels because, for a given hardness, the finegrained steel is tougher, residual stresses are lower, there is lessdistortion, quenching cracks are less prevalent and the steel has lessretained austenite. For this reason,-

melting practices are used which will produce a fine grained steel. Thepractices include additions prior to and during tapping which tend toinhibit austenitic grain growth in the final product.

Aluminum is most commonly used to produce fine grained steels because itis both effective and inexpensive. Normal aluminum additions forproducing a fine grained plain carbon steel range from 1 lb./ ton ofsteel to 5 lb./ ton of steel depending upon the grade of steel and thesteelmaking practice. A residual aluminum content of .02 to .O5% isdesired to produce a fine grain structure. With alloy steels theresidual aluminum may be as low as .015% to produce a fine grainstructure.

and silicon rather than as ferrovanadium. The alloys disclosed in mycopending application Ser. No. 502,380, filed on even date herewith areespecially adapted for this purpose.

I have, alsddiscovered that if the alloy of vanadium and siliconcontains small amounts of one or more carbide and nitride formingelements, for example, columbium, titanium, zirconium and boron, evensmaller additions of vanadium produce a fine grained steel. When analloy including carbide and nitride forming elements is used, the steelremains fine grained after heating to temperatures in excess of 1700 F.A vanadium-.iron-silicon alloy including some of the elementsspecifiedfabove is termedcomplex V-Fe-Si and is disclosed in mycopending application Ser. No. 502,3 80. if

Basically my method consists in treating molten steel Prior to teemingby ad i g all a minum-ir nsilicon alloy and a vanadium-iron-siliconalloy to the molten metal. The addition of aluminum and vanadium in theform of silicon. alloys as distinguished from aluminum metal andferrovanadium produces a fine grained steel which may be treated attemperatures well within the austenitic range while maintaining a finegrain size.

In order to determine the grain size of; steel produced by my process,A181 1040 steel heats were melted in a 300 pound induction furnace andvarious additions were made to the molten metal after it was tapped intoa ladle. The ladles of steel were then teemed into 4" x 4" x 24" molds.The resulting ingots were identified and forged to 1% square bars.Sections were cut from these bars for the McQuaid-Ehn grain size testsand the ASTM grain size was determined after heat treatment.

In melting the steel heats, Armco scrap was melted in the inductionfurnace, the slag removed and suflicient silicon added as 50% FeSi tolower the FeO content and leave a residual of 0.10% silicon in the bath.Sufiicient pig iron was added to give .40% carbon and when in solution,electrolytic manganese and ferrosilicon were added to produce therequired composition. The heats were then tapped at 2900 F. into theladle and treated.

The analysis of the steels after treatment met the AISI 1040specification and had the following composition ranges:

Percent C .4l-.43 Mn .82.88 P .0.012 S .017.019 Si .24-.32

The treatment in the ladle in each instance was to de-Calcium-ferrosilicon alloy 16.0% Ca, 57.8% Si, 'bal.

, essentially Fe. Aluminum-silicon-iron alloy 19.0% A1, 38.9% Si, bal.

essentially Fe. Aluminum 99.5% Al. Ferrovanadium 75.15% V, bal.essentially Fe. V-Fe-Si (Ht. 28.00% V, 51.48% Si, bal.

essentially Fe. V-FeSi (Ht. 28) 51.34% V, 24.82% Si, bal.

' essentially Fe. Complex VFe-Si (Ht. 16) 29.55% V, 46.12% 2.31% Cb,2.04%

1.98% Zr, 0.11% B, 1.75% Al, 1.59% Ba, 2.34% Mn, bal. essen- Si, Ti,

4 It will be observed that the addition of .02% aluminum to AISI 1040steel, either as aluminum or as an alloy containing aluminum and siliconproduced a coarse grained steel.

EPQAMPLE 2 Additional ingots were made and processed in the mannerdescribed in Example 1. The ladle additions and the grain size resultsfor the individual heats are listed below.

Heat No. Ladle Additions McQuaid-l'ghn Grain Size, 1,100" F 148.OZFVgVAI as alumlnum+.06% V as 7, 8 plus 5, (Ya. 21C .02% Al asAlumlnum-\-.04% V as Duplex 5% plus l-4. 21B .0%9Z,V.:Al asAl-Fe-Sl+.04% V as Duplex 5-8 plus 1-4.

EXAMPLE 3 Additional ingots were made and processed in the mannerdescribed in Example 1. The ladle additions and the grain size resultsfor the individual heats are listed below.

Heat No. Ladle Additions McQuaid-Ehn Gr Size, 1,700 F.

240 .02% Alas Aluminum-+01% V as Duplex 5-8 plus 1-4.

V-Fe-Si (Ht. 15). 24B. .02% Al as AlFeSi+.04% V as 7, 8 and finer.

V-Fe-Sl (Ht. 15).

When the vanadium was added to the steel as the V- Fe-Si alloy, a finegrained steel was P oduced at the lower vanadium level but, as shown bya comparison of heats 24B and 24C, only when the aluminum was added asan alloy containing silicon. It is pointed out that the grain size forHeat 246 is the same as for Heats 21B and 21C in Example 2.

EXAMPLE 4 Additional ingots were made and processed in the mannerdescribed in Example 1. The ladle additions and the trally Fe. grainsize results for the individual heats are listed below.

McQuald-Ehn Grain Size Heat N0. Ladle Additions 3011 .02% Al as A1-FeSi+.005% V as 7, 8 and finer, few 6's Duplex 7, 8 and finer plus V-Fe-Si(Ht. l5 "s.

D .02% Al as Al-Fe-Si+.0025% V as do 7, 8 and finer, few 6s.

Complex V-Fe-Si (Ht. l6).

29D .02% Al as Al-Fe-Si+.04% V as V-Fe- 7, 8 and finer Duplex 7, 8 andfiner plus Sl (Ht. 28). l-3S.

31C .02% Al as Al-Fe-Si+.04% V as do 7,8 and finer, iew fis.

Complex V-Fe-Si (Ht. 16).

The following examples will serve to illustrate the eifect of variousladle additions on the McQuaid-Ehn. grain size of AISI 1040 steel.

EXAMPLE 1 The ladle additions exclusive of the 2 lbs. of calcium-fer-'rosilicon alloy per ton of steel which was added to each ladle and theresulting grain size for the individual heats are listed below:

Heat No. Ladle Additions l\lcQ,uaid-Ehn Graln Size, 1,700" F..

5A .02% Alas Aluminum With an addition of .02% aluminum as an alloycontk'aun'ing silicon, extremely low additions of vanadium as theV-Fe-Si alloy or as the complex V-Fe-Si alloy containing small amountsof other elements produced fine grained steel. The steels treated withthe complex V-Fe-Si alloy were also fine grained at higher temperatures.To show that the fine grain at 1800 F. is a characteristic of thecomplex V-Fe-Si alloy used and not the level of the vanadium addition,the higher vanadium additions of .04% as each of the two vanadium alloyscontaining silicon are included in the example. In all of the abovetests the core of the carburized specimens had the same grain size asthe grain size recorded for the case.

The addition of the calcium-ferrosilicon deoxidizer prior to thealurninum-iron-silicon alloy addition is not essental but assures moreuniform aluminum recoveries. Other deoxidizers could be used if desired.

The above examples demonstrate that the aluminum must be added as analloy of aluminum containing silicon, and that the vanadium must beadded as an alloy of vanadium containing silicon. Example 4 alsodemonstrates that when the molten steel is treated according to my novelmethod using the complex vanadium alloy disclosed in my copendingapplication, the amount of vanadium necessary to assure fine grain sizeis far less than the amount required when other vanadium alloys areused.

In addition it has been demonstrated that minute amounts of vanadium,when added as the novel complex vanadium silicon alloy containing smallamounts of elements such as columbium, titanium, zirconium, boron, etc.,and in accordance with my novel method, will produce a fine grainedsteel which steel will be fine grained at higher temperatures such asused for high temperature carburizing. The amounts of the effectiveelements other than vanadium in the .0025% vanadium addition (Ht. 30D)were extremely minute and, except for vanadium, are too low to bedetermined quantitatively in the finished steel. Based on the knowledgeof grain size control of steel, such levels of addition, either singlyorin combination, would not have any effect on the grain size of thesteel.

My invention may be embodied Within the scope of the appended claims.

I claim:

1. The method of producing fine grained steel comprising adding tomolten steel prior to teeming aluminum as an alloy containing aluminumand silicon and adding vanadium as another alloy containing vanadium andsilicon and teeming said molten steel.

2. The method set forth in claim 1 wherein said aluminum addition isless than about 02%.

3. The method set forth in claim 1 wherein said vanadium addition isabout .-O05%.

4. The method set forth in claim 1 wherein said aluminum addition isless than about .02% and said vanadium addition is about .005

5. The method set forth in claim 1 wherein said alloy containingvanadium and silicon includes small amounts of columbium, titanium,zirconium and boron.

6. The method set forth in claim 1 wherein said alloy containingvanadium and silicon includes small amounts of columbium, titanium,zirconium and boron, and said vanadium addition is .0025%.

References Cited UNITED STATES PATENTS 2,221,783 11/1940 Critchett eta1. 5 8 2,280,283 4/1942 Crafts 755 8 X 2,291,842 8/ 1942 Strauss 75-5 82,296,938 9/ 1942 Lytle 755 8 BENJAMIN HENKIN, Primary Examiner.

DAVID L. RECK, Examiner.

